Use of insert type lathe tools

[JAParticipant @ja]

In my old age I now need three hands, one to steady myself, when using a bench grinder. I have ground all my lathe tools from HSS blanks but the operation is now very frightening. Therefore, I have decided to generally use cutting tools with inserts about which I know nothing. I am wading through websites, magazines, books, discussion groups, forums etc trying to get information before making a purchase on Monday but this has confused me. I want to make the purchase directly and not through Amazon or eBay.

The lathe in question is a Myford Connoisseur with a maximum spindle speed of 3,000rpm. Ideally I would like to use speed below 1000rpm because everything runs smoother. Flood cooling is available. Most of my turning and boring involves brass, bronze, steel including stainless, cast iron and good aluminium. The cuts I take are usually quite light and use left hand knife cutter for diameter and facing, boring tools, form cutters and parting off. I realise that I will not replace all my HSS tools. I use a quick change tool post so the insert holder would have 8mm or 10mm shank. As for the size of the work, anything that can fit in the lathe.

Questions etc

1.      It appears that two materials are available for insert, carbide and a chromium steel. I would like to use chromium steel. Is this sensible?

2.      Inserts come in many shapes. Which are the most useful?

3.      Can I use a parting off holder and insert in a rear tool post?

4.      If necessary, can I use carbide at low cutting speeds?

5.      An explanation of the nomenclature used for inserts would be useful.

6.      Recommendations on suppliers would be use. I would prefer to use industrial suppliers.

7.      In case I have missed something, comments would be welcome.

JA

 

[Thor 🇳🇴Participant @thor]

Tools with carbide inserts can be used at low speeds, I use inserts intended for Aluminium (and its alloys) even for cutting mild steel. They work well.

I use a carbide insert parting off tool in the rear tool post of my lathe.

Carbide Insert designation explained.

Thor

[MacolmParticipant @macolm]

As long as your lathe is adequately rigid and in good and well adjusted condition, you should be able to run sharp style carbide inserts at any speed down to near zero. Inserts designed for aluminium are mostly of this type, and work well even when cutting most steels. However, avoid inserts primarily for industrial production of tough materials which usually are not sharp enough for home use, being designed to stand up to greater cutting forces in a much more rigid machine – some indeed will have zero or negative rake.

You may dislike Amazon and Ebay, but they do offer the possibility to try things out cheaply so as to decide your best options. Carbide inserts are probable cheaper than other materials, but unfortunately there are millions of individual items. It will get easier once you get a feel for the characteristics.

[JasonBModerator @jasonb]

1. Use Carbide

2. CCMT and CCGT will do for both turning and boring so you only need keep one shape in stock

3. Yes upside down in the back is OK for parting

4. Yes low surface speeds are OK, 1000rpm max will be OK even on slamm diameters

5. UK code numbers may be better than the US based little machine shop

https://www.cutwel.co.uk/blog/learn-the-turning-tool-iso-code-system?srsltid=AfmBOooYyIhFcyzo4XQfJ8ezwaEYvuSKqYr3bLq1QXgX_w6_nNtAtvCk

https://www.cutwel.co.uk/blog/understanding-iso-code-system-turning-tools?srsltid=AfmBOoryp-u7NjRG64dlr6qICbGU2HkvsK_e6Ez3wpGMAEculZ_qqoip

6 I would go with APT, they sell inserts in twos or 10s. Holders I have had good us eof Glanze ones (Chronos)

https://www.shop-apt.co.uk/

Home

7. I would strongly suggest you use the **GT inserts (bright silver) which are intended for non ferrous and stainless as they work well on all materials particularly when light cuts are required.

[David SeniorParticipant @davidsenior29320]

I would endorse everything that Jason has said. I buy most of my inserts from APT.

I think you will be pleasantly surprised how good the tips are on almost any material.

Dave

[duncan webster 1Participant @duncanwebster1]

I get most of mine from https://jbcuttingtools.com/ , often seen at exhibitions. If you want to stick with HSS you could try a Tangential tool holder, but make sure of import duties and handling charges before ordering as I don’t think they have a UK supplier any more. I reckon you could use the sharpening device one handed.

[DiogenesParticipant @diogenes]

Yes, what Jason says.

I mostly use 10mm shank holders with a few 12s in both the ML7 and GH600 (280 swing). One can buy larger boring bars that use the same tips and a 16 or 20mm is a useful thing if you have a suitable toolpost

Be wary of ‘touching off’ stationary work especially with one hand on the chuck – they really don’t like ‘backwards-pressure’ on the cutting edges and in the early days it’s easy to chip them before one breaks ingrained habits.

[JAParticipant @ja]

One further question. Can carbide inserts take an intermittent cut such as turning a square bar or fly cutting?

JA

[JasonBModerator @jasonb]

Yes

[VicParticipant @vic]

I’ve bought most of my recent inserts from Amazon and eBay, they’re often much cheaper and often top industrial makes. JB cutting tools are good as well though.

You don’t say how big your lathe is and the capacity for tools? I’ve got a 8 1/2” x 14” lathe and find the 12mm shank tools a really good fit. Both tools bought from JB, one is double sided for left and right turning. The most economical tool though takes Double sided triangular inserts so you get 6 cutting tips per insert, many other types only give you 2 (and the inserts are often the same price!)

I gave up on insert type parting tools as they’re not so good on softer materials and my lathe isn’t really rigid enough for them. I went with T shape HSS parting blades which are very easy to sharpen.

I use polished carbide inserts for turning aluminium and mild steel. They’re ok on interrupted cuts (I use one in my Flycutter) on aluminium but they wouldn’t survive long on steel.

Agreed about the Tangential Tool. I made my own and I can use the sharpening jig I made for it one handed. Probably the easiest HSS tool to sharpen apart from a parting tool.

Much depends on what sort of materials you intend to cut and what your budget is.

[JasonBModerator @jasonb]

JA says he has a Myford.

[JAParticipant @ja]

Thank you all for your replies. I now have a far greater understanding of the subject.

JA

[MacolmParticipant @macolm]

The one thing you must avoid with carbide is allowing any part of the material to get into tension. In particular, make sure the edge in contact with the work is never even slightly below centre. It is then quite easy to pull off the edge.

[HuubParticipant @huub]

On my hobby lathe, I use inserts for finishing operations. On my lathe that is still heavy cutting. I use the G typed inserts for aluminum when all other types don’t work. These sharp G-type inserts cut very well using light cuts.

When you start using insert, you will break/chip a lot of these pretty fast. So start by buying the cheapest ones you can find on E-bay or AliExpress. Once you stop breaking them, it may be time to move to a better quality insert.

Give the CCMT060204 VP15TF (finishing grade) from KOESOTR or LYYZ a try. These are also available in DCMT or TCMT types.
I use the G-type CCGT060204-AK from KORLOY (AliExpress) but they are probably fake. Nevertheless, they do a great job.

 

 

[Nigel Graham 2Participant @nigelgraham2]

I can see a potential problem with being prepared to sacrifice the cheap ones: is the breakage due to some error in setting, speed/feed etc; or an inherently weak insert?

Nevertheless they are not cheap if you buy from the reputable dealers as I think they purchase from industry-suppliers. I use JB Cutting tools and buy at the exhibitions. Since I use HSS as well I’ve not yet run out! I have used Greenwood Tools (was it?) in the past but they’ve disappeared.

Sellers such as the Beattys know our applications and can advise you.

 

I have tried an insert parting-tool but even in a rear-toolpost would not recommend it without being absolutely sure of the rigidity, squareness of set-up etc. They look inherently too weak for a lightweight machine of relatively low rigidity, and a commercially-made holder that introduces a big side overhang between blade-holder and tool-post.  I have had more problems with insert parting tools than with HSS blades, and now use only HSS ones.

On the other hand, grinding an HSS parting-tool so it will work properly is not as straightforwards as it seems. They do not want any angle across the end, as that makes the chip wider than the kerf. The parting inserts are not only of optimum geometry, they also have a chip-folding groove to move the swarf from the wall of the cut.

 

I have also found with some materials, an HSS tool can give a better finish – but to be fair this tends to be on steel of unknown grade probably not made for fine work anyway. (A lot of my material is “pre-loved”, as they say, so always a gamble.)

Some bronzes can be very unco-operative too, but I have not found a definite difference between using carbide or HSS on them.

 

As for speeds  – carbide inserts will work any sensible speed. I have recently cut a number of screw-threads using a carbide tool, on a Myford ML7 on back-gear, with no problems.

There is a widespread belief that insert tooling has to be run at great speed; but that arose because it can, not because it has to. These are really industrial tools intended for quoted lives in tens of minutes at maximum production rates on rock-solid machines with very precise material and tip choice, machine control, flood-coolant etc; but are happy sauntering along on an elderly hobby lathe with manual feed.

It is the combination of material, tool material and shape, and speed/feed setting; that is the key, not all-out rush.

 

 

[DiogenesParticipant @diogenes]

I use a number of parting tools including a flat ‘blade-type’ carbide insert one (?general designation SGIH) 19mm high and 2mm wide (the inserts are ‘GTN 2’). These blades /tips are widely available in a range of depths and work well in a rear toolpost on a Myford.

If your machine is still tight and stands ‘parting-from-the-front’, you might look at an MGEHR ‘grooving’ tool (MGEHR 1010 2 (ie. 10mm sq shank, for 2mm tips)). One can buy both square and full radius double-ended tips, they have some lateral stability and can be used to profile with care (say cleaning up a small crank journal) – they will part material up to, er, over an inch (?28mm) – a useful tool for all kinds of work.

My personal preference is for the 2mm nominal width tooling, though 3mm and up are available should you prefer those.

 

 

 

[JasonBModerator @jasonb]

Same as Diogenes, I use a GTN-2 for larger work, MEGHR for medium parting but mostly for it’s 1mm radius and for small >12mm parting, small grooves and undercutting threads  I use a 1mm wide parting insert. The HSS parting tools seldom come off the rack. All front loading.

[Kiwi BlokeParticipant @kiwibloke62605]

JA – I’m sorry to hear that you’re having problems with the use of a grinder. The advice about high-positive rake inserts is all good, but they’re still quite pricey, fragile, and need expensive holders. I must have invested hundreds of pounds into the tipped-tooling technology over the years, but it’s not a cure-all, and the choice of tips is bewildering enough to drive you crazy – and/or empty your pocket.

Decades ago, I discovered that my Super 7 (young, in excellent, tight condition, and adjusted properly) just couldn’t cope with one particular ‘blunt’ Sumitomo insert that was sold to model engineers. Eventually, the cause turned out to be the minute clearance in the mandrel cone bearing: chatter was certain unless the bearing was adjusted so tightly that end thrust from drilling from the tailstock slowed the lathe dangerously. Myfords aren’t very rigid. However, the same insert worked perfectly on my Emco Maximat Super 11, which has rolling headstock bearings. Trial and error is an expensive way to select inserts…

To address the root of your problem, can you re-arrange the grinder so you can use it sitting down, and, if needed, arrange arm rests? HSS grinding is a gentle art, and, as you know, HSS works well in the home workshop. As I age, I find myself doing more from a chair…

[Bo’sunParticipant @bosun58570]

Another vote for the 2mm wide insert parting tool.  Just make sure it’s set as perfectly “on centre” as you can and square to the work, slow steady feed with lubricant/coolant.  Back the tool out and clear the swarf if it looks like its building up.

[Kiwi Bloke]

On Kiwi Bloke Said:

JA –

To address the root of your problem, can you re-arrange the grinder so you can use it sitting down, and, if needed, arrange arm rests? HSS grinding is a gentle art, and, as you know, HSS works well in the home workshop. As I age, I find myself doing more from a chair…

I have to say that I do an awful lot from lab stools. Another for the bench grinder which is well away from all other tools, is an escape option

 

 

On Macolm Said:

The one thing you must avoid with carbide is allowing any part of the material to get into tension. In particular, make sure the edge in contact with the work is never even slightly below centre. It is then quite easy to pull off the edge.

Does this mean you should forget about taking a reverse facing cut, that is withdrawing the tool from the work? With HSS I have found that this gives a good finish.

JA

[Clive FosterParticipant @clivefoster55965]

For carbide speeds and feeds always check the data book. A major advantage of buying brand name tools is that there is a book with reliable data.

As has been said the sharp ones intended for aluminium can be treated like HSS but edge fragility can be an issue.

Some industrial types have speed and feed recommendations very similar to HSS. Usually ones intended for manual machine tools of the Colchester Student. Master, Triumph sizes so smaller lathes may not have the strength to deal with the larger tip radius and slightly blunter edge that is much more resistant to handling damage.

For example my basic, as in I always have one mounted up,  carbide tool is the Sandvick CNMG 12 04 08 – 23.

According to my spreadsheet book call outs for steel and stainless steel are:-

Cutting speed :-   80 – 100 ft / min or 25 – 30 m / min

Feed :-    5 – 9 thou / rev or 0.14 – 0.24 mm / rev

Depth of cut  :-    14 – 142 thou  or 0.36 – 3.6 mm

As I recall matters I chose those as my starter insert over 20 years ago because the speeds and feed were in familiar HHS territory and an E-Bay seller was offering 4 or 5 boxes and a holder at a silly low price. Trying to use them on a Southbend Heavy 10 was a bit optimistic tho’. The heftier P&W and Smart & Brown lover them.

On the other hand I misread the steel cutting speed specifications for a Indexia DCMT 11 T3 08-PF as 345 – 470 m / min as ft/ min! Actually 1130 – 1545 ft/m. Ooops. They mean it too.

Box was probably silly cheap ‘cos most E-Bay surfers actually read the specifications and decided they couldn’t run them.

The beast doesn’t start to perform below about 800 or 900 ft / min depending on exact steel specifications. Get it in the sweet spot, usually a bit over 400 ft / min, with blue or amber chips flying and the finish is to die for. Hydraulic cylinder rod class.

Clive

[JasonBModerator @jasonb]

Yes you can withdraw the tool taking a light cut without problem.

 

I woudl not wprry too much about book speeds, unless you have a CNC lathe that increases spindle speed as the diameter when facing decreases you will only have the right surface speed for one part of a facing cut.

But as a good rule of thumb carbide inserts can run 3 time sas fast as HSS so where you may have used 100ft/min with HSS, 300ft/min will do for carbide cutting steel. thats 30m vs 100m for the metrically minded.

[HollowpointParticipant @hollowpoint]

I have a 2mm tipped parting tool by Kennemetal which I use on my Boxford at the front. It uses a much less common N151 tips but its the absolute dogs! It seems to cut anything I throw at it with ease and the tip life with genuine tips is incredible! I have a box of 10 tips and I’m still one the first one after about 18 months of use! At that rate I probably have a lifetimes supply. Haha.

[duncan webster 1Participant @duncanwebster1]

I have one of those insert parting tools sold by Greenwood years ago as the answer to myford parting issues. A wide industrial blade screwed to a 3/8″ sq bar which goes in the toolholder. The tip is 2.5mm wide. It certainly improved the performance of my ML7. The downside is the countersunk screws in shear, which don’t work well, and the extra overhang on the small myford size Dickson QCTP. One if these days I’ll get round to adding some dowells which might help

I suspect the main feature is that the chip is curled in by the groove in the top of the insert and so doesn’t get jammed in the kerf. I’ve seen pictures of tee shaped HSS blades with a hollow top which might do the same.

[JA]

On JA Said:

One further question. Can carbide inserts take an intermittent cut such as turning a square bar or fly cutting?

JA

3/8″ thick steel with CCGT 060204

Rod

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